They ran out of food a couple of days ago, and ran out of water just today, so naturally they're pretty desperate.
Out on the water, one of them spies a genie's lamp, and they both frantically paddle towards it.
One of them pull out the lamp and rubs it, and lo and behold, a genie pops out!
“Will ye grant us tree wishes mister?” the Irishman pleads.
“I'd love ta, but this old genie's barely enough for just the one. So wish carefully.”
Quickly, one of the men calls out, “I wish the ocean'd turn ta Guinness!”
“Consider it done.” The genie and the lamp disappear, and the entire ocean changes from water to beer.
The second Irishman looks at the first, stunned, then finally manages, “Ya fockin' idiot! Now we have ta piss in the boat!”